1. Field of the Invention
Priority is claimed on Japanese Patent Application No. 2002-381816, filed Dec. 27, 2002, the content of which is incorporated herein by reference.
The present invention relates an angle detection optical system to an angle detection apparatus, an optical signal switch system, and an information recording and reproduction system.
2. Description of Related Art
Conventionally, an angle detection apparatus is known that irradiates light from a predetermined position onto a reflective surface used for detection that is provided on a portion of a detection object, and then, by detecting the position of the reflected light, detects the angle from the predetermined position of the detected object.
For example, in Japanese Patent Application Unexamined Publication (JP-A) No. 8-227552 (pages 2–3, FIGS. 1–2) an optical apparatus is disclosed that is provided with a detecting apparatus whose light receiving surface is divided into four sections and that is designed to detect an angle between a disk (i.e., a disk shaped information recording medium) and an optical head in order to write information onto the disk, and to detect the thickness of a disk protective layer. The detection apparatus that is divided into four sections irradiates light from an optical element onto the disk and then receives reflected light from the disk. It then outputs electrical signals corresponding to the quantity of light received by the respective light receiving surfaces. The center position of the reflected light relative to the division center of the light receiving surfaces is then detected by relative ratios of the output electrical signals. The angle of the disk is then detected from the size of the positional shift in the radial direction of the disk. The thickness of the disk protective layer is detected from the size of the positional shift in the tangential direction of the disk.
In Japanese Patent Application Unexamined Publication (JP-A) No. 11-144274 (pages 3–4, FIGS. 6, 9) a deflection angle detection apparatus is described in which angle detection light is irradiated onto the rear surface of a galvanomirror, the reflected light therefrom is separated into two luminous fluxes using a luminous flux splitting unit that has a splitting surface in which the reflectance changes in accordance with the light angle of incidence, the light quantities of the two luminous fluxes are detected independently using respective optical detectors, and the deflection angle of the galvanomirror is detected from the difference in the outputs. This technology enables the detection sensitivity to be improved by calculating the difference of A−B using a detected output A, which increases as the angle of incidence relative to the separation surface decreases, and a detected output B, which decreases as the angle of incidence relative to the separation surface decreases.
In addition, for example, optical signal switch systems used in optical communication and information recording and reproduction systems that use lasers are known as systems that are equipped with the above type of angle detection apparatus and make use of the deflection angle control of light deflection elements.
However, in the technology described in JP-A No. 8-227552, because the relative ratios of outputs of the light receiving surface that is divided into four sections are used, the detection sensitivity at the center position of the light receiving spot and the detection range are restricted by the size of the spot diameter, and these two are in a trade-off relationship with each other. Accordingly, in order to broaden the detection range while improving the sensitivity of the detection of the disk inclination angle, it has been necessary to increase the distance between the disk and the optical device and to alter the amount of change of the light receiving position of the reflected light relative to the amount of change in the inclination angle.
In the technology described in JP-A No. 11-144274, the detection sensitivity of the inclination angle is improved, but the angle of incidence is in a linear relationship with the reflectance. In addition, because the characteristics of the reflection film directly affect the detection accuracy, the detection accuracy deteriorates unless the reflection film is manufactured with a high level of precision.
A high degree of reliability is demanded in an optical signal switching system and information recording and reproduction system that use the above described conventional angle detection apparatus as a deflection angle control apparatus. Therefore, there are cases when a backup angle detection apparatus is provided in case of a failure in the angle detection apparatus being used. Moreover, because deflection angle control that is highly accurate and is performed over a wide range is sought from these apparatuses, there are cases when the control operation is performed in two stages, namely, coarse tuning and fine tuning.
In such cases, it is only possible to provide two apparatuses in parallel for the above described type of conventional angle detection apparatus.